public static void LinearRampDemo(string dir)
{
Report.BeginTimed("linear ramp demo");
var width = 1920;
var height = 1080;
var barHeight = height / 4;
var line = new byte[width].SetByIndex(
i => Col.ByteFromDouble((double)i / (double)(width - 1)));
// write an image with linear red, green, blue, and gray ramps
var linearImage = new PixImage <byte>(Col.Format.RGB, new V2i(width, height));
var linVol = linearImage.Volume;
linVol.SubVolume(0, 0, 0, width, barHeight, 1).AsMatrixWindow().SetByCoord((x, y) => line[x]);
linVol.SubVolume(0, barHeight, 1, width, barHeight, 1).AsMatrixWindow().SetByCoord((x, y) => line[x]);
linVol.SubVolume(0, 2 * barHeight, 2, width, barHeight, 1).AsMatrixWindow().SetByCoord((x, y) => line[x]);
linVol.SubVolume(0, 3 * barHeight, 0, width, barHeight, 3).SetByCoord((x, y, c) => line[x]);
linearImage.SaveAsImage(Path.Combine(dir, "linear-ramp.tiff"));
Report.End();
}